1. Field of the Invention
The present invention is related to a microcapsule type electrophoresis display panel with a color filter. The panel has a structure in which a microcapsule layer is sandwiched between a pair of electrode plates facing each other, one of the electrode plates being a transparent substrate with a color filter layer and an electrophoresis ink is enclosed in a microcapsule in the microcapsule layer. The use of a color filter suitable for the above components can improve the quality of an image of a multi color display panel.
2. Description of the Related Art
In recent years, due to the development of information devices, various information displays are also being developed. A CRT or a liquid crystal using a backlight are main stream display panels of variable information. However, when a light emitting type display such as a CRT or a liquid crystal display using a backlight is watched for a long time, the human has eye becomes strained. Therefore, such a display is not suitable for reading a document or the like for a long time.
In addition, a screen in a liquid crystal display without a backlight becomes very dark due to the use of a polarizing plate which reduces visibility. Further, a display image of these displays does not have memory characteristics. If an electric energy supply is stopped, a display image suddenly disappears. Therefore a display which does not cause eye strain, has excellent visibility, low power consumption and images having memory characteristics is required.
As a reflection type display device which rarely causes eye strain, for example, an electrophoresis type display panel is proposed as shown in patent document 1, the electrophoresis display panel having a pair of mutually facing electrodes and an electrophoresis display layer arranged between the electrodes. This electrophoresis type display panel displays a character or an image by reflection light. This principle is the same as in printed paper. Therefore, the display panel rarely causes eye strain and is suitable for viewing for long periods.
The principle of this electrophoresis display panel is as follows. A voltage is applied to a dispersion liquid in which an electrically charged particle is dispersed. Thereby, the charged particle moves, and image display becomes possible. A microcapsule type electrophoresis display panel in which a colored charged particle is enclosed in a microcapsule and the microcapsule is arranged between a pair of mutually facing electrodes has advantages such as low driving voltage and highly flexibility and is being used practically and continuously developed.
This electrophoresis panel is suitable as a substitute for a display of an information portable device such as a PDA (personal digital assistance) or an electronic book which are predicted to be used widely, or a printed matter such as a newspaper, a book, a magazine and a poster, or displaying a hard copy on paper from a printer. The electrophoresis panel generally has a structure of two color displays (white and black display). However, in recent years, multi-color colorization is required for the purpose of displaying the magazine or a color printed matter.
In order to realize a multi-color colorization of the electrophoresis panel, the following ideas are disclosed. For example, using an electrophoresis particle of multi-color equal to or more than two colors, the particle is arranged in a predetermined pixel by patterning using photolithography (patent document 2) or by photolithograph and ink-jet (patent document 3). In addition, in patent document 4, a cell frame for receiving a microcapsule is formed in advance and a plurality of microcapsules are surely arranged in a desirable position, thereby display of a plurality of colors becomes possible. However, arranging multi-color microcapsules at a predetermined pixel requires more processes and is complex. Therefore, there are actually many technological difficulties.
Therefore, in patent document 5, a color filter substrate is attached to a white and black electrophoresis display panel. Thereby, it is possible to display multi colors without accurate position adjustment between a microcapsule and a pixel. However, in this method, because a separately manufactured color filter is attached on a white and black reflection type electrophoresis display panel, it is necessary to arrange an adhesive for the attachment. Therefore, display brightness is low and attachment of a color filter is difficult which reduces productivity. Further, because the distance between a color filter layer and an electrophoresis display layer is large, there is a disparity in color depending on the viewing angle. An advantage of electronic paper, which is not influenced by the viewing angle, disappears.
Then, the inventors of the present invention found that, in the case where a microcapsule ink is directly formed on a transparent electrode layer of a color filter, display brightness and a viewing angle can be improved. However, the influence of a change in a film thickness of a color filter layer on reflection density becomes larger. An application liquid in which a microcapsule is dispersed has a very high thixotropy. Therefore, non-uniformity of an application liquid which is generated due to non-uniformity of an underlying surface does not become flat or uniform even in a state before drying. Therefore, flatness of a color filter in a observer side, the color filter being an underlying surface of a transparent electrode layer to be coated by a microcapsule, is important in order to display using a color filter with a high definition without non-uniformity over the entire display screen.    Patent document 1: JP-B-S50-015115    Patent document 2: JP-A-2002-365668    Patent document 3: JP-A-2003-156770    Patent document 4: JP-A-2003-295234    Patent document 5: JP-A-2003-161964
The present invention was made by considering the above background. The object of the present invention is to provide a multi color display panel with excellent uniform display quality in which reduction of display brightness and narrowing of a viewing angle are resolved.